Structured lighting is a well known technique for use in extraction of 3D information from a scene. The extraction of 3D information is based on the projection of a known lighting pattern on a scene, and capturing of the resulting image with a camera of the scene. The technique works on the basis of disparity (as when a stereo-camera is used), with a distance (often called the baseline) between the camera and a projector that projects the lighting pattern. As a result of this disparity, one can determine the depth of an object (seen from the camera). Similar to a stereo-camera, such a system can estimate depth, but as we project lighting structures (patterns), the system also works on uniform objects, which is not the case for a stereo camera. Therefore, structured light systems provide much more reliable depth estimation than stereo vision systems.
A key step in 3D information extraction is the determination where features of the lighting pattern are projected on the object by the projector. This is sometimes called “decoding. A decoding technique is described in an article by Gumholdt et al in an article titled “Image-based motion compensation for structured light scanning of dynamic surfaces” (IJISTA(2008) 434-441). In this technique a plurality of different structured lighting patterns is used successively, the time dependence of the pixel intensity being used to identify the plane from the projector that intersects the object at the pixel. In its simplest form, this technique assumes that the object does not move. If object movement cannot be excluded, motion compensation according to a motion vector is used to map an object point to the same pixel in a series of images. Gumholdt mentions that detection of motion of stripes from the structured lighting pattern can be used to determine the required motion vector, but Gumholdt prefers a more robust technique, wherein special reference lighting patterns are used to obtain images that can be correlated to determine the motion vectors. However, these techniques are still not completely robust.